linux-kernel - Re: [PATCH v9 5/8] block: set FOLL_PCI_P2PDMA in __bio_iov_iter_get

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Date:   Mon, 5 Sep 2022 17:48:05 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-mm@...ck.org
Cc:     Christoph Hellwig <hch@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Martin Oliveira <martin.oliveira@...eticom.com>,
        Chaitanya Kulkarni <ckulkarnilinux@...il.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH v9 5/8] block: set FOLL_PCI_P2PDMA in
 __bio_iov_iter_get_pages()

On 8/25/22 08:24, Logan Gunthorpe wrote:
> When a bio's queue supports PCI P2PDMA, set FOLL_PCI_P2PDMA for
> iov_iter_get_pages_flags(). This allows PCI P2PDMA pages to be passed
> from userspace and enables the O_DIRECT path in iomap based filesystems
> and direct to block devices.

Oh great, more O_DIRECT code paths. :)

> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> ---
>  block/bio.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 969607bc1f4d..ca09d79a0683 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1200,6 +1200,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  	unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt;
>  	struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
>  	struct page **pages = (struct page **)bv;
> +	unsigned int flags = 0;

It would be nice to name this gup_flags, instead.

>  	ssize_t size, left;
>  	unsigned len, i = 0;
>  	size_t offset, trim;
> @@ -1213,6 +1214,10 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  	BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
>  	pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
>  
> +	if (bio->bi_bdev && bio->bi_bdev->bd_disk &&
> +	    blk_queue_pci_p2pdma(bio->bi_bdev->bd_disk->queue))
> +		flags |= FOLL_PCI_P2PDMA;
> +
>  	/*
>  	 * Each segment in the iov is required to be a block size multiple.
>  	 * However, we may not be able to get the entire segment if it spans
> @@ -1220,8 +1225,9 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  	 * result to ensure the bio's total size is correct. The remainder of
>  	 * the iov data will be picked up in the next bio iteration.
>  	 */
> -	size = iov_iter_get_pages2(iter, pages, UINT_MAX - bio->bi_iter.bi_size,
> -				  nr_pages, &offset);
> +	size = iov_iter_get_pages_flags(iter, pages,
> +					UINT_MAX - bio->bi_iter.bi_size,
> +					nr_pages, &offset, flags);
>  	if (unlikely(size <= 0))
>  		return size ? size : -EFAULT;
>  

Looks good. After applying Christoph's tweak, and optionally the gup_flags
rename as well, please feel free to add:

Reviewed-by: John Hubbard <jhubbard@...dia.com>


thanks,

-- 
John Hubbard
NVIDIA